1. Field of the Invention
The present invention relates to a rubber composition for use in golf balls; tires including tire outer parts such as treads and sidewalls, and tire inner parts such as carcasses, belts, and beads; industrial products such as rubber vibration isolators, belts, hoses, and rubber vibration suspensions; and shoes such as men's shoes, women's shoes, and sports shoes. More particularly, it relates to a golf ball rubber composition for use in golf balls, and a golf ball.
2. Description of the Related Art
Polybutadiene for use in golf balls as rubber base material is required to have high hardness, high rebound and impact resistance as well as excellent processability. Patent Document 1 (JP-A2004-43714) discloses a technology that provides improvements in high hardness, high rebound, and impact resistance. In general, however, a higher Mooney viscosity improves the rebound but worsens the processability. In contrast, a wider molecular weight distribution improves the processability but worsens the rebound. In a word, there is an antinomy between the improvements in processability and rebound. For the purpose of achieving the compatibility of processability and rebound, improvements in the property of polybutadiene have been tried and various proposes have been provided. For example, Patent Document 2 (JP-A 63-275356) and Patent Document 3 (JP-A2-177973) disclose polybutadienes having a high Mooney viscosity and a wide molecular weight distribution and synthesized in the presence of a Ni-based catalyst.
Further methods are disclosed to employ two types of rubber with different rubber physical properties. For example, Patent Document 4 (JP-B 6-80123) discloses polybutadiene rubber with a low Mooney viscosity and polybutadiene rubber with a high Mooney viscosity.